EFFECTS OF LOADING RATE AND SPECIMEN CONFIGURATION ON THE DUCTILE-BRITTLE TRANSITION IN POLY(PROPYLENE)

To gain more insight into the fracture behavior of poly(propylene) (PP), specifically on the loading rate dependent ductile-brittle transition a fracture mechanics methodology was developed and applied. For this purpose, loading rate and geometry effects (various relative crack length values, SENB vs. C(T) specimens, and plain-sided vs. side-grooved specimens) on the fracture behavior of three PP types were investigated by performing fracture toughness tests over 6 decades of loading rates. Using different definitions of J-integral for data reduction, which properly account for the temperature rate and geometry dependence of the fracture behavior of plastics, a procedure is proposed to better characterize the ductile-brittle transition in the semi-brittle crack extension region and in terms of an “embrittlement point ” at high loading rates. Comparing the various PP types investigated, differences in the ductile-brittle transition behavior on the loading rate scale of up to 4 orders of magnitude were determined. Moreover, it was found that for SENB specimens the “embrittlement point ” depends on the relative crack length, a/W